A fiber reinforced polymer (FRP) is a composite material including a polymer matrix reinforced with fibers such as glass, carbon, or plastic to improve the strength, rigidity, and impact resistance of the polymer. The properties of an FRP are dependent on the fiber length, fiber distribution, and fiber orientation within the polymer matrix. To optimize one or more properties of the FRP, the fibers present in various samples of the FRP can be measured. The fibers can be separated from the polymer matrix using heat. The fibers can then be spread on the platen of a flat-bed style scanner. The scanner can provide an image for use in measuring the lengths of the fibers present. If the fibers are transparent or near transparent, for example, when the fibers are glass or plastic, light from a light source below the platen can pass through the fiber, reflect from a cover of the scanner, and pass back through the fiber without providing sufficient contrast within the image to distinguish between the fibers for image processing.